A switching regulator typically employs a high-side metal-oxide semiconductor field effect transistor (MOSFET) (HS FET) and a low-side MOSFET (LS FET) to switch power between the HS FET and LS FET by a switching control signal and to provide current to an output inductor. In other cases, the MOSFETs can be replaced with bipolar transistors or other switching/linear pass devices. The switching regulator typically employs feedback of the output to an error amplifier where the feedback is compared to a stable reference voltage to maintain a constant output voltage. If the output voltage falls below or rises above the reference voltage, the switching frequency and/or duty cycle of the switching signal varies so as to maintain a constant output voltage. A low-dropout (LDO) regulator is a DC linear voltage regulator which can operate with a very small input-output differential voltage. The main components are a power FET and a differential amplifier (error amplifier). One input of the differential amplifier monitors a percentage of the output and the second input to the differential amplifier is from a stable voltage reference (bandgap reference). If the output voltage falls below or rises above the reference voltage, the drive voltage to the power FET changes so as to maintain a constant output voltage.
LDO regulators and switching regulators are widely used in integrated circuits (ICs). An LDO regulator may not be very power efficient but can have substantially low system implementation costs. A switching regulator can be power efficient, but because the circuit requires an inductor, it will be more expensive than an LDO regulator and need more printed circuit board (PCB) area than an LDO regulator. From a cost perspective, an LDO and a switching regulator would not likely be fabricated on the same IC chip. Also there are pin limitations to implementing both an LDO regulator and a switching regulator on the same IC chip. However, in certain situations, in certain applications, it is desirable to have a dual regulator type circuit that allows for configuring the dual regulator type circuit as either an LDO or a switching regulator. For example, some applications may require an LDO regulator for lower system cost and better noise performance, while other applications may require a switching regulator to have better power efficiency, especially in battery powered implementations. Usually an IC with a dual regulator needs an additional pin that can be used to define a particular mode of the regulator. This pin is either pulled to a particular voltage or connected to ground to define the setting. However, this implementation increases IC chip pin outs and costs.